Description:Valves elongate-rectangular, with sub-parallel dorsal and ventral margins and a slightly concave posterodorsal margin giving a triangular posterior termination in lateral view. Fossae deep, slit-like, becoming more equidimensional towards the anterior and posterior margins. Sexual dimorphism conspicuous; males proportionally slimmer both in lateral and dorsal view, and with a compressed posteroventral marginal area in both valves. Distal process of male copulatory appendage subtriangular with a produced, curled, posterior free corner and an elongate lamellar extension on the distal (anterior) free corner.

Habitat:A sublittoral species living at depths down to 75 metres.

Remarks:Neale (1973) has given a thorough review of both recent and fossil records of this species, and subsequently (1975) published further illustrations of valves and appendages.

Distribution:Found most commonly in the northern part of the British Isles; according to Neale (1975) it is widely distributed from Shetland and S Norway to the Bay of Biscay. It does not live in the Mediterranean.